The present invention is directed toward the monitoring of plant assets and, more particularly, toward a system and method for monitoring the performance of a heat exchanger using a heat exchanger model.
Heat exchangers are widely used in a variety of industrial processes to transfer heat between a process fluid and a thermal transfer fluid. This transfer of heat may be performed to heat or cool the process fluid or to change the state of the process fluid. There are three main types of heat exchanger, namely recuperative, regenerative and evaporative. Of these three types, the recuperative type is the most common. In a recuperative heat exchanger, the process fluid and the thermal transfer fluid are separated by structures, such as tubes or plates, through which heat is transferred from one fluid to the other fluid. The transfer of heat between the two fluids occurs through conduction and convection. The most common types of construction for recuperative heat exchangers are shell and tube, plate and spiral. Operatively, recuperative heat exchangers can be single phase or two-phase and can be parallel flow, counter flow, or cross flow.
Regardless of their particular construction or operation, all recuperative heat exchangers are subject to fouling, which is the formation of deposits on the surfaces of the heat transfer structures. Fouling can occur through crystallization, sedimentation, chemical reaction/polymerization, coking, corrosion and/or biological/organic material growth. Fouling reduces the efficiency of a heat exchanger by constricting fluid flow and reducing the heat transfer coefficients of the heat transfer structures. Accordingly, heat exchangers are periodically cleaned to remove fouling. Typically, the cleaning of a heat exchanger is performed according to a predetermined maintenance schedule. Between such scheduled cleanings, however, the efficiency of the heat exchanger may deteriorate significantly. As a result, the heat exchanger may operate inefficiently for a significant period of time before the heat exchanger is cleaned, thereby resulting in a waste of energy and an increase in operating cost. Accordingly, it is desirable to monitor the efficiency of the heat exchanger during its operation.
Conventional systems and methods for monitoring the efficiency of heat exchangers require special fouling sensors and/or specific information about the construction of the heat exchangers. Examples of such conventional heat exchanger monitoring systems and methods are disclosed in U.S. Pat. No. 5,992,505 to Moon, U.S. Pat. No. 5,615,733 to Yang and U.S. Pat. No. 4,766,553 to Kaya et al. In all of these patents, the efficiency of a heat exchanger is determined from a ratio between the heat transfer coefficient at a baseline time period and the heat transfer coefficient at a measured time period, wherein the heat transfer coefficients are calculated using, inter alia, the area and thickness of the heat transfer surface(s). The Moon patent further requires a special fouling sensor having a metal wire wound in a spiral around a body having heating wires extending therethrough. Thus, conventional heat exchanger monitoring systems and methods must be specially customized for the heat exchangers to which they are applied and often require special equipment, such as fouling sensors, to be mounted on or near the heat exchanger.
Based on the foregoing, there exists a need in the art for a system and method for monitoring the performance of a heat exchanger, wherein the system and method do not require specific information about the heat exchanger and do not require special fouling sensors to be mounted on or adjacent to the heat exchanger. The present invention is directed to such a system and method.